The present invention relates to a signal determination apparatus that determines an analogue signal and a temperature determination apparatus that performs determination of a temperature based on an analogue signal of a thermistor.
In a case where various kinds of controls are performed by detecting a signal, a microcomputer is often used as a control circuit. Usually, I/O ports of the control circuit (the microcomputer) of which the number corresponds to the number of input and output signals to be used are required.
Therefore, sometimes, it is not possible to perform efficient reduction of the number of pins in a case where a ready-made microcomputer is used. In a case where, for example, a microcomputer having 20 pins is expected to be used and the number of I/O ports necessary for implementation is greater than the number of I/O ports specified for the microcomputer by one, it may happen that a microcomputer having 30 pins, which is one-rank upper than the microcomputer having 20 pins, have to be used. This may cause not only increase of the cost, but also 9 pins of unused terminals to be wasted, and the unused terminals may cause an erroneous operation due to noise or the like. Therefore, a technique of sharing of a signal line or an I/O port has been offered.
For example, Patent Document 1 discloses a technique of a microcomputer in which a pulse signal of an encoder and a temperature signal of an inner part of the encoder are acquired by a single signal line drawn from the encoder without increasing the number of signal lines. In the technique, when detection of a temperature of the encoder is requested to a CPU of a controller to which the encoder is connected, the CPU detects a binary voltage of a signal input to a first port of the CPU via a signal line. When the binary voltage is in a high level, a second port of the CPU is connected to the ground. A voltage division resistor is provided in a preceding stage of the second port of the CPU. The CPU measures a voltage of an A/D input port different from the first and second ports so as to compute the temperature of the encoder based on a voltage value of the voltage of the A/D input port. At that time, a voltage Va divided by a resistance value of a thermistor and a resistance value of the voltage division resistor is input to the A/D input port of the CPU. The CPU computes the resistance value of the thermistor based on the voltage value of the voltage Va and calculates out the temperature of the inner part of the encoder based on a characteristic curve of the thermistor.
In another technique, Patent Document 2 discloses to fetch signals of a plurality of thermistors into an A/D port by a selecting operation of the thermistors by virtue of a single switching operation.
Patent Document 1: JP-A-2007-121074
Patent Document 2: JP-A-2003-121270
Meanwhile, it is possible to reduce the number of signal lines drawn from the encoder by the technique disclosed in Patent document 1. That is, the technique is effective to a case where a plurality of pieces of data are superposed in the signal of the inner part of the encoder. However, there is no description about a technique that the signal of the inner part of the encoder is in common use with a signal from another device. Therefore, another technique is required. In addition, the technique disclosed in Patent document 2, relates to detection of a signal from a device, the signal having an analogue signal characteristic, i.e., detection of a temperature. However, Patent document 2 does not teach a function of detecting signals having an analogue signal and a digital signal which are mixed therein at a single port.